FIG. 1 is a perspective view showing a schematic structure of a traction drive power transmission device 100 of this kind. The traction drive power transmission device 100 comprises a driving section 103, composed of a driven roller 102a and a driving roller 102b, and a guiding section 104, composed of a pair of driven rollers 102a and 102a, wherein a shaft 101 which is made of metal and is formed in a cylindrical shape is held with high bearing stress between the driven roller 102a and the driving roller 102b of the driving section 103 and between the driven rollers 102a and 102a of the guiding section 104. Each of the driven rollers 102a and the driving roller 102b is made of metal, is formed into a substantially cylindrical shape of which periphery is curved into an arc shape in the axial direction, and is arranged such that its central axis are perpendicular to the axis of the shaft 101.
The traction drive power transmission device 100 acts as follows. As the driving roller 102b is rotated in a state that the shaft 101 is held between the driven roller 102a and the driving roller 102b of the driving section 103, the rotational force is transmitted from the driving roller 102b to the shaft 101 by frictional force generated on contact faces of the driving roller 102b and the shaft 101, whereby the shaft 101 moves in the axial direction. Such traction drive power transmission device 100 has advantages that, as compared to ball screws and the like, the structure is simple so that it is easy to increase the moving speed of the shaft 101 by changing the diameter of the driving roller 102b and/or changing the rotational speed and therefore has been used in a broad range of fields.
In the traction drive power transmission device 100 having the aforementioned structure, a lubricant film is formed on contact portions of the shaft 101 with the driven roller 102a and the driving roller 102b by applying lubricant such as grease or oil on sides of the shaft 101 so as to prevent wear of the driven roller 102a, the driving roller 102b, and the shaft 101. However, the conventional traction drive power transmission device has the following problems:
(1) Since the lubricant is applied on the outer surface of the shaft 101 periodically by hands using a brush or the like, the work operation of applying the lubricant is troublesome.
(2) Since each of the driven roller 102a and the driving roller 102b is formed to have a periphery composed of a single arc or a combination of a plurality of arcs in the axial direction, the contact portions of the peripheries of the driven roller 102a and the driving roller 102b with the periphery of the shaft 101 are only the central portions of the arcs. However, as the lubricant is applied to the periphery of the shaft 101 by hands, the lubricant is applied not only to the contact portions of the shaft 101 with the driven roller 102a and the driving roller 102b but also to other portions than the contact portions. Accordingly, the lubricant is consumed wastefully.
(3) As the lubricant is applied by hand to the periphery of the shaft 101 of which section is circular, the applied lubricant flows downward and drips because the property of retaining the lubricant is poor. Accordingly, there is a problem that the lubricant at the contact portions easily becomes insufficient so that the lubricant must be applied frequently. There is also a problem that the dripped lubricant soils a floor and the like so as to worsen working conditions.
The present invention has been made in view of the aforementioned problems and the object of the present invention is to provide a traction drive power transmission device in which lubricant can be stably applied to contact portions of a shaft with rollers over an extended time period so as to prevent the lubricant from becoming insufficient at the contact portions and to prevent the lubricant from being wastefully consumed so that the working conditions is not worsened by soiling a floor and the like.